Blood pressure may be defined as cardiac output x systemic vascular resistance. It is the pressure of the blood exerted against the walls of the arteries as the blood flows through the artery. Blood pressure should always be assessed as part of the initial assessment of an infant or child and then as the child’s condition dictates. It may give an indication of cardiac function in the presence of known cardiac disease and renal function in the presence of chronic renal insufficiency. Blood pressure is recorded as systolic (contraction of left ventricle and ejection of blood into arterial vessels) over diastolic (recoil of the artery and relaxation of the heart).

It is important to note that children have the ability to compensate in the presence of a decreased cardiac output so hypotension is a late and pre-terminal sign of decompensating shock. It will require immediate treatment and the instigation of life support for the child.

Blood pressure is recorded and monitored in two ways:

• non-invasive
  
• invasive.

Non-invasive blood pressure measurement is performed either manually with a sphygmomanometer or an automated device. Manual recording is the gold standard in non-invasive measurement of blood pressure. However, it can be challenging to record the blood pressure of a young child with a sphygmomanometer due to their lack of cooperation and the difficulties in auscultating a brachial pulse in their cubital fossa.

The most important aspect in recording an infant’s or a child’s blood pressure is choosing the correct cuff size, whether their blood pressure (BP) is being recorded manually or electronically. The cuff size should not be determined by the manufacturer’s sizing on the cuff but by the child’s arm dimensions. ‘undercuffing’ – too narrow or too short a bladder, can lead to overestimation of BP, and ‘overcuffing’ – too wide or too long may lead to underestimation. The cuff should be two-thirds of the distance from the elbow to the shoulder or the upper thigh, and the bladder of the cuff should cover 100% of the circumference of the arm (Figure). The cuff size used should be documented so continuity of care can be provided.

• Explain the procedure to the child and family, telling them how it will feel.
  
• Wash your hands.
  
• Ensure the infant/child is resting/sitting quietly for as long possible. Ideally this should be between 1–3 minutes. The child might wish to sit on their parent’s lap. BP should be recorded before any other anxiety-inducing procedures. Use diversion techniques.
  
• Remove restrictive clothing on arm/leg.
  
• Select correct size cuff.
  
• Ensure arm is supported and positioned at heart level.
  
• Apply cuff snugly around arm, ensuring that the centre of the bladder covers the brachial artery.
  
• Place sphygmomanometer at eye level.
  
• Palpate for brachial pulse.
  
• Close air escape valve and inflate cuff until radial pulse can no longer be palpated. Continue to inflate cuff to another 20 mmHg higher than estimated systolic pressure.
  
• Place diaphragm of stethoscope gently over pulse point of brachial artery, ensuring it is not tucked under edge of cuff.
  
• Release air valve slowly to deflate the cuff-2–3 mmHg per second.
  
• Note the first Korotkoff’s sound – a clear tapping sound, and record as systolic value. Record the diastolic pressure as the fourth Korotkoff sound – a low-pitched, muffled sound for children up to 12 years of age. Record the fifth Korotkoff’s sound – the disappearance of all sound for children aged 13–18 years.
  
• Remove cuff and replace child’s clothing.
  
• Document readings on observation chart and in care records, noting limb, position, cuff size and method of measurement.
  
• Wash hands and clean equipment and store correctly.

• You must be familiar with the operating instructions of the device available. This device must be validated.
  
• Apply the correctly sized cuff to the child’s upper limb.
  
• Inflate as per instructions. It is important to keep the child as still as possible as the machine will pump to a pre-determined level initially, so if the child is upset and moving their limb, most automated devices tend to pump to a higher pressure on subsequent inflation attempts which may distress the child even more.
  
• Allow the cuff to deflate, note the digital reading on the display.

Invasive recording involves the insertion of an arterial line into the child which is then connected to a monitoring system. This is only practised in critical care area normally.